This invention relates generally to heaters for water tanks, and more particularly to a heater for installation in the drain plug opening of a water tank.
Commercially available water tanks typically include a drain opening in their side to drain the tank so that it can be moved or refilled. The sizes of the drain plug openings vary depending on the manufacturer of the tank. Currently available are heaters that can be used in tanks with drain openings greater than 1.75 inches in diameter, such as the DPH-15 manufactured by the assignee of this patent application. A drain opening of this size permits the passing through of the electrical plug. However, many tanks have drain openings smaller than 1.75 inches which do not allow the passage of the standard sized electrical plug. U.S. Pat. No. 6,151,448 shows a device that can be used in water tanks with smaller drain openings. This device includes an intermediate connector having a small diameter located in the power cord between the heater body and the electrical plug. When the heater is installed in the drain opening of a tank, the electrical plug is disconnected from the heater body by disconnecting the intermediate connector. One end of the intermediate connector is then passed through the drain opening and the electrical plug is reconnected by connecting the other end of the intermediate connector to the end of the intermediate connector passed through the drain opening. Therefore, the electrical plug can have a larger dimension than the drain opening. The intermediate connector, however, increases the problems of short circuiting or electrical shock, particularly when the connector is exposed to water, increases the possibility of accidental disconnection, and increases the cost of the device.
The present invention provides a drain plug heater. One embodiment of the drain plug heater includes a heating element, a housing, and a power cord. The housing includes a mounting portion adapted to be inserted into a drain opening of varying sizes. The power cord includes a reduced sized three-prong electrical plug that will pass through drain openings of varying sizes including openings less than one inch in diameter.
In one embodiment, a water heater for installation in a drain plug opening of a water tank comprises a housing, a heating element extending into the housing, and an electrical power cord. A proximal end of the power cord is secured to the housing and a distal end of the cord is secured to a three-prong plug configured for insertion into a standard electrical power outlet. The cord is formed of at least three conductive lines extending continuously from the housing to the three-pronged plug. A portion of the housing has a diameter of less than approximately one inch and is configured to extend through the drain plug opening for use in securing the housing to the water tank. The three-pronged plug has a diameter which is substantially equal to, or less than, the diameter of that portion of the housing.
In one embodiment, the housing comprises a cupped portion. In this embodiment the heating element extends from the cupped portion into the water tank.
In one embodiment, the portion of the housing configured to extend through the drain plug opening has a diameter of approximately xe2x85x9e inch. In this embodiment, the diameter of the three-pronged plug is substantially equal to the diameter of that portion of the housing (i.e., the diameter of the three-pronged plug is approximately xe2x85x9e inch).
In one embodiment, the portion of the housing configured to extend through the drain plug opening is threaded. In this embodiment, a nut is provided for securing the housing to the water tank. The nut is threaded to engage the portion of the housing which extends through the drain plug opening. The nut is further configured to allow for passage of the three-pronged plug through a central opening of the nut.
In one alternative embodiment, the central opening of the nut is configured to engage the portion of the housing which extends through the drain plug. In this embodiment, the central opening is provided with at least one notch to facilitate passage of the three-pronged plug through the opening. In an alternative embodiment, the central opening of the nut is provided with at least one projection extending into the central opening. In this embodiment, the projection engages threads or other structures on the housing portion to secure the housing to the water tank.
In certain embodiments of the invention, the nut configured to engage the housing to secure the housing to the tank has a continuous circumferentially-extending body. In certain embodiments, the nut has a central opening which has a diameter slightly larger than the diameter of the three-pronged plug.